High-frequency heating apparatus having electromagnetic wave agitating device

ABSTRACT

An agitation device for high-frequency electromagnetic waves in a high-frequency oven has at least one pair of planar rotary blades of metal extending in radially opposite directionsfrom a hub part and fabricated, together with the hub part, from a single strip of sheet metal into a staggered or stepped shape in which the blades respectively lie in mutually different offset planes and present minimum profiles with respect to air resistance during rotation, the blades thereby rotating through mutually different paths and imparting effective field agitation to prevent occurrence of a high-frequency standing wave and to render uniform the distributive state of the high-frequency waves applied to the oven interior.

United States Patent 1 3,692,967 Hashimura [4 Sept. 19, 1972 [54]HIGH-FREQUENCY HEATING 2,813,185 11/1957 Smith ..2l9/10.55 APPARATUSHAVING 3,364,332 1/ 1968 Reftmark ..2l9/10.55 ELECTROMAGNETIC WAVEAGITATING DEVICE Primary Examiner-J. V. Truhe Assistant Examiner-Hugh D.Jaeger [72] Inventor Tetsuo Hashimm Kawasakl Japan Attorney-Robert E.Burns and Emmanuel J. Lobato [73] Assignee: Tokyo Shibaura DenkiKabushiki Kaisha, a. k. a. Tokyo Shibaura [57] ABSTRACT grgg aggKawasaki-Sm An agitation device for high-frequency electromagnetic wavesin a high-frequency oven has at least one Flled! 1970 pair of planarrotary blades of metal extending in radi- [21] Appl No: 78,357 allyopposite directionsfrom a hub part and fabricated, together with the hubpart, from a single strip of sheet metal into a staggered or steppedshape in which the [52] US. Cl. ..2l9/10.55 blades respectively lie inmutually different offset [51] 111i. Cl. ..H05b 9/06 planes and presentminimum profiles with respect to [58] Fleld of Search ..219/ 10.55 airresistance during rotation, the bl thereby rotat ing through mutuallydifferent paths and imparting ef- [56] References Cited fective fieldagitation to prevent occurrence of a high- UNITED STATES PATENTSfrequency standing wave and to render uniform the distributive state ofthe high-frequency waves applied 3,626,136 12/1971 Funahashi ..219/l0.55to the oven him-ion 3,526,737 1/1970 Black ..2l9/l0.55 3,431,381 3/ 1969Anderson .219] 10.55 7 Claims, 3 Drawing Figures HIGH-FREQUENCY HEATINGAPPARATUS HAVING ELECTROMAGNETIC WAVE AGITATING DEVICE BACKGROUND OF THEINVENTION therein thereby to prevent the generation of a highfrequencystanding wave.

In general, most of the agitation devices provided in the heatingchambers of heating devices of this class have blades or vanes oftwisted shape. In spite of the difficulty in and high cost offabrication in providing this twisted shape, the effectiveness of thesevanes in producing the objective electrical-field agitation is notsatisfactorily high. Furthermore, the twisted shape of the blades givesrise to a stirring of the air within the chamber, which'is not the truefunction of the field agitator.

SUMMARY OF THE INVENTION It is an object of the present invention toprovide, in a high-frequency heating apparatus, an agitation devicehaving high effectiveness in agitation action and having low air dragduring operation.

Another object of the invention is to provide an agitation device of theabove stated character which is of simple yet strong construction andcan be produced at low cost.

According to the present invention, briefly sum marized, there isprovided a high frequency heating apparatus consisting of a housingstructure having an access opening, a heating chamber provided withinsaid housing structure, a generator fixed to the interior of saidhousing structure for supplying high frequency electromagnetic waves tothe interior of heating chamber, a door for closing the access opening,and characterized by an agitation device comprising a motive-powerdevice, a rotatable shaft coupled at one end thereof to the motive-powerdevice to be driven thereby, and a fan structure fixed to the other endof the shaft and having at least two planar rotary blades of metal andof configurations such that the rotational paths thereof are mutuallynoncoincident and such that minimum air drag is encountered by the .fanstructure in rotation, said fan structure being disposed within theheating chamber at a position for effectively agitating thehigh-frequency electromagnetic waves therewithin thereby to prevent thegeneration therein of a highfrequency standing wave and to renderuniform the distributive state of the high-frequency electromagneticwaves.

The nature, principle, and utility of the invention will be more clearlyapparent from the following detailed description with respect topreferred embodiments of the invention when read in conjunction with theaccompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING In the drawing:

FIG. 1 is a side elevation, with a part cut away, showing the essentialparts of an electronic oven in which one example an electric-fieldagitating device according to the invention is installed;

FIG. 2 is a perspective view showing one example of a fan structurehaving two blades of an agitation device of the invention; and

FIG. 3 is a perspective view showing another example of a fan structureof the invention, which structure has four blades.

DETAILED DESCRIPTION Referring to FIG. 1, the electronic oven showntherein has an external housing structure 1 comprising an outer case 2and an inner case 4 with a space 3 interposed therebetween. The outercase 2 is provided at its front wall with access an opening 5 having adoor 6 hinged at its lower edge to the lower part of the structure 1.The inner case 4 and the door 6 define a heating chamber, which in thisexample is a cooking chamber 7. The inner case 4 and door 6, of course,are made of electroconductive materials such as metals.

Through the upper wall or ceiling of the cooling chamber 7, the outputpart 9 of high-frequency electromagnetic wave generator comprising amagnetron 8 is directed into the chamber to introduce high-frequencywaves thereinto to heat an object 10 such as an item of food placed inthe chamber.

An agitation device 11 according to the invention as describedhereinafter is supported at the upper central part of the cookingchamber 7 by a vertical shaft or driving spindle 12 passing through theceiling of the chamber and coupled at its upper end to a rotary drivemotor 13.

This agitation device 11 is essentially a stirrer fan or fan structure15 fabricated from a strip of metal sheet into a staggered or steppedshape as shown in FIG. 2 wherein two planar blades 14 and 19 extendradially outward in opposite directions from a central hub part 16 inmutually different offset parallel planes, the blade 14 being offset bya distance d above the plane of the hub part 16 and the blade 19 beingoffset by distance e below the hub part. The fan structure 15 is fixedat its hub part 16 to the lower extremity of the spindle 12 by anysuitable means such as a screw fastening, a welded joint, or a calkingjoint.

The above mentioned distances d and e are not equal. Because of thestepped shape of the fan structure '15, the distances a and b of theblades 19 and 14 from the bottom or floor of the cooking chamber 7 arealso unequal. Another feature of the fan structure 15 is that the blades14 and 19 are not twisted, and all parts thereof are positioned topresent the minimum profile with respect to air resistance duringrotation whereby the fan structure incurs minimum air drag duringoperation.

The electronic oven of the above described organization including theagitator according to the invention operates in the following manner.First, an object to be heated such as an item of food 10 is placed incooking chamber 7, and door 6 is closed, whereupon the oven is in itsoperable state. When a switch (not shown) is closed, magnetron 8 andmotor 13 start to operate substantially at the same time, magnetron 8supplying high-frequency electromagnetic waves into cooking chamber 7,and motor 13 rotating fan structure through driving spindle 12.

Thus, blades 14 and 19 of fan structure 15 rotate smoothly withoutencountering any appreciable resistance from the air within chamber 7and thereby agitate the electromagnetic waves therein. As a result, thegeneration of a high-frequency standing wave is effectively prevented,and, at the same time, the distributive state of the high-frequencywaves in chamber 7 is rendered uniform. A feature of the invention isthe stepped shape of fan structure 15 whereby it operates with higheffectiveness in accomplishing electric-field agitation.

While the fan structure 15 of the agitator 11 in the above describedexample comprises two blades formed from a single strip of sheet metal,a plurality of such fan structures can be assembled with their hub partsin stacked arrangement to form a multiplebladefan structure. Such astructure is even more effective in accomplishing field agitation.

In one example of such a multiple-blade fan structure as illustrated inFIG. 3, two fan structures 17 and 18, each of stepped shape with offsetblades, are combined to form a four-bladed fan structure. The offsetdistances of the blades from the hub part thereof are all different, sothat the blades rotate in respectively different planes. That is, thedistances designated by reference characters f, g, h, and i are alldifferent.

The number of blades of the fan structure can, of course, be increasedfurther to produce further effectiveness in field agitation.Furthermore, the offset distances of a single two-blades structure 15can be made equal.

From the foregoing description, it will be apparent that because of thesimple construction of the field agitator according to the presentinvention, it can be readily fabricated at low cost.

lclaim:

1. In a high-frequency heating apparatus having means therein defining aheating chamber wherein objects to be heated are placed; a generatoroperable to generate high-frequency electromagnetic waves and supplysame into said heating chamber; and an agitation device for agitatingthe high-frequency electromagnetic waves comprising a rotatable shaftextending into said heating chamber, rotary drive means connected tosaid shaft for rotationally driving same, at least two planar bladeshaving high-frequency energyreflective surfaces connected to said shaftand extending radially outwardly therefrom in axially spaced-apartrelationship with respect to the shaft axis and cooperative together toeffectively agitate the high-frequency electromagnetic waves therebypreventing the formation of high-frequency electromagnetic standingwaves within said heating chamber in response to rotation of said shaft,and means positioning said planar blades on said shaft in mutuallydifferent parallel planes to present the minimum surface profile withrespect to air resistance encountered during rotation of said bladesthereby minimizing air drag during operation of the agitatin device.

2. In fire apparatus according to claim 1 wherein said last-mentionedmeans comprises means positioning each of said planar blades on saidshaft for rotation in mutually parallel and distinct planes.

3. In the apparatus according to claim 1; wherein said at least twoplanar blades comprise a pair of planar blades extending radiallyoutwardly from said shaft in opposite directions; and a hub connectingsaid pair of planar blades in mutually offset planes to said shaft.

4. In the apparatus according to claim 3; wherein said hub and pair ofplanar blades are fabricated from a single strip of sheet metal.

5. In the apparatus according to claim 1 wherein said at least twoplanar blades comprise two pairs of planar blades, each pair of planarblades extending radially outwardly from said shaft in oppositedirections; and a hub connecting each pair of oppositely extendingplanar blades in mutually offset planes to said shaft.

6. In the apparatus according to claim 10; wherein each hub and theplanar blades connected thereto are fabricated from a single strip ofsheet metal.

7. In the apparatus according to claim 1; wherein said at least twoplanar blades comprise a plurality of planar blades extending radiallyoutwardly from said shaft in circumferentially spaced-apartrelationship; and wherein said means positioning said planar blades onsaid shaft comprises means positioning said plurality of planar bladesfor rotation in mutually different horizontal planes.

1. In a high-frequency heating apparatus having means therein defining aheating chamber wherein objects to be heated are placed; a generatoroperable to generate high-frequency electromagnetic waves and supplysame into said heating chamber; and an agitation device for agitatingthe high-frequency electromagnetic waves comprising a rotatable shaftextending into said heating chamber, rotary drive means connected tosaid shaft for rotationally driving same, at least two planar bladeshaving high-frequency energy-reflective surfaces connected to said shaftand extending radially outwardly therefrom in axially spacedapartrelationship with respect to the shaft axis and cooperative together toeffectively agitate the high-frequency electromagnetic waves therebypreventing the formation of highfrequency electromagnetic standing waveswithin said heating chamber in response to rotation of said shaft, andmeans positioning said planar blades on said shaft in mutually differentparallel planes to present the minimum surface profile with respect toair resistance encountered during rotation of said blades therebyminimizing air drag during operation of the agitating device.
 2. In theapparatus according to claim 1 wherein said last-mentioned meanscomprises means positioning each of said planar blades on said shaft forrotation in mutually parallel and distinct planes.
 3. In the apparatusaccording to claim 1; wherein said at least two planar blades comprise apair of planar blades extending radially outwardly from said shaft inopposite directions; and a hub connecting said pair of planar blades inmutually offset planes to said shaft.
 4. In the apparatus according toclaim 3; wherein said hub and pair of planar blades are fabricated froma single strip of sheet metal.
 5. In the apparatus according to claim 1wherein said at least two planar blades comprise two pairs of planarblades, each pair of planar blades extending radially outwardly fromsaid shaft in opposite directions; and a hub connecting each pair ofoppositely extending planar blades in mutually offset planes to saidshaft.
 6. In the apparatus according to claim 10; wherein each hub andthe planar blades connected thereto are fabricated from a single stripof sheet metal.
 7. In the apparatus according to claim 1; wherein saidat least two planar blades comprise a plurality of planar bladesextending radially outwardly from said shaft in circumferentiallyspaced-apart relationship; and wherein said means positioning saidplanar blades on said shaft comprises meanS positioning said pluralityof planar blades for rotation in mutually different horizontal planes.